Transducer driver circuit controlled by saturating cores



F. A. MAVTHAMEL,

TRANSDUCER DRIVER CIRCUIT CONTROLLED BY SATURATING CORES Original Filed Jan. 19', 1966 v v v v 5 50 1 F'LAVIUS A. MATHAMEL "AT TORNEY United States Patent Int. Cl. H041 /12 US. Cl. 178-17 11 Claims ABSTRACT OF THE DISCLOSURE A system including a transducer for converting a mechanical motion into an electrical signal. The system includes a single saturable core, a single winding thereon, a permanent magnet, a movable magnetic shunt, and a switching member. At its opposite ends, the winding is connected to a source of current and at one of its ends to the switching member such that the winding is common to two circuits. When the switching means is opened, current flows in one direction through the winding and the core is saturated in one sense. This resets the core automatically upon the opening of the switching member. The magnet is positioned such that it magnetically places a bias on the core opposing its being switched to its other or set state, thus inhibiting the output of a pulse from the winding. When the switching member is turned on, current flows through the winding in a reverse direction and causes the polarity of the core to reverse and become saturated such that when the shunt is moved to an ineffective position there is a pulse output from the winding.

This application is a continuation of my application entitled Transducer, Ser. No. 521,662, filed Jan. 19, 1966, now abandoned.

This invention relates to apparatus for converting physical motion into an electrical signal, and more particularly, to driving and sensing circuitry for such transducers.

In the co-pending application of Ser. No. 816,643 filed Apr. 16, 1969, a continuation of Ser. No. 433,359 to Flavius A. Mathamel, filed Feb. 17, 1965, and assigned to the same assignee as this application, a transducer is disclosed which is especially suitable for use in keyboards. In this transducer a permanent magnet biases a ferromagnetic core. Driving pulses applied to the ferromagnetic core are capable of switching the core from one state to the other in the absence of the biasing flux from the permanent magnet, but are unable to switch the core when the core is biased by the permanent magnet.

A magnetic shunt is moved between the permanent magnet and the core whenever a key in the keyboard is depressed so as to remove the biasing flux. When the core is not biased, the switching pulses switch the core from one state to the other causing a voltage to be generated in the sensing winding on the core indicating that the key has been depressed. In the alternative, the permanent magnet may be attached to the keystem of the key so that it is moved away from the core when the key is depressed, causing output pulses to be generated in the sensing winding. In this embodiment a shunt for the flux is not needed. A third alternative is to move the permanent magnet which is attached to the keystem or other suitable keyboard member away from the core and into a magnetic shunt. This latter method improves the resolution of the transducer.

It is desirable that the drive circuitry for switching the ferromagnetic core from one state to the other be simple, reliable and inexpensive. Because of this, semiconductor drivers are normally used in such switching applications. However, a ferromagnetic core presents a varying impedance to a driver whenever it is switched by the driver from one state to the other. Accordingly, the driver must have a high output impedance in order to operate efliciently. But power transistors normally have a relatively low output impedance. If resistors are added to increase the output impedance of the transistor, power is wasted by being dissipated in the resistor. Also, expensive transistors must be used because high voltage transients are generated as the cores are switched. The transistors must be able to withstand these voltage transients. Furthermore, drivers of this type ar expensive because they must either provide AC pulses or else use two DC drivers.

In the patent application to Narendra M. Shukla, Ser. No. 472,425, filed July 16, 1965, now Pat. No. 3,446,984, and assigned to the same assignee as this application, a relatively inexpensive driver is disclosed. In this driver, current flows through an inductor and through a resetting winding on the core, slowly resetting the core. The current flowing through the reset winding flows to ground through a semi-conductor switch. Whenever this semi-conductor switch is closed, the current flowing through the inductor is interrupted and the energy stored in the inductor discharges through an alternate path that flows through the set windings on the core. This current switches the cores to the other state.

While this driver is relatively inexpensive because it incorporates transient protection and has an automatic reset mechanism, it still requires two windings on the ferromagnetic core and an additional inductor tostore energy. It is desirable to reduce the cost of the driver even further because of the large number of such drivers that may be used in computing apparatus. Accordingly, it is an object of this invention to provide such a simplified transducer and current driver combination.

It is a further object of this invention to provide a ferromagnetic transducer which only requires one winding on the ferromagnetic core and which also incorporates an automatic reset mechanism.

It is a further object of this invention to provide a current driver in which transients are reduced in the switching of the cores used in the transducer.

In accordance with the above objects, a transducer is provided having a ferromagnetic core, a permanent magnet, a movable shunt, a Zener diode, a transistor and a voltage source. The single Winding on the ferromagnetic core is connected at one end to a resistor which is connected to the voltage source, to the output terminal, and to the cathode of the Zener diode and on the other end to another resistor which is connected to the voltage source and to a driver transistor. The anode of the Zener diode is grounded. The current flowing from the voltage source passes through the winding in one direction and then to ground through the Zener diode when the driver transistor is off. It resets the core while it is doing this. When an input pulse causes the driver transistor to conduct an alternate path to ground is formed and the current from the voltage source flows in the opposite direction through the winding on the core setting the core.

The Zener diode has typically a 5 volt breakdown point so that th voltage at the output terminal remains at 5 volts while the core is being reset. When the core is set by turning on the driver transistor, the set voltage is clamped to 5 volts by the Zener diode so that the output remains constant. However, if the permanent magnet inhibits the core so that it does not switch, the Winding around the core appears as a short circuit, causing the voltage at the output terminal to drop to the collector on voltage of the driver transistor which is near ground. The only time that this condition is present is when the shunt is not placed between the permanent magnet and the core. This happens when a key in the keyboard, for example, is depressed lifting the shunt away from the permanent magnet.

The invention and the above noted and other features thereof will be understood more clearly and fully from the following specific description when considered with reference to the accompanying drawings in which:

FIG. 1 is a perspective drawing illustrating the manner in which an embodiment of this invention is used;

FIG. 2 is a schematic circuit diagram of an embodiment of the invention; and

FIG. 3 is a graph of a plurality of curves having common abscissae of time and individual ordinates of current or voltage.

In FIG. 1 a perspective view of part of a keyboard using an embodiment of the invention is shown having a ferromagnetic core 10, a permanent magnet 12 positioned near the ferromagnetic core, and a shunt 14 adapted to be moved between the ferromagnetic core and the permanent magnet 12 whenever a key 16 on the keyboard is depressed. When the key 16 is depressed, it pushes the key lever 18 down so that the projection 20 spaced along the bottom side of the key lever 18 slide between the selected code bails 22.

Each of the code bails 22 fits into a slot of a bellcrank 24 that has a shunt 14 positioned on one end in such a manner that when the code bail is in a position nearest the end of the carriage, the shunt 14 is positioned away from the ferromagnetic core 10 and the permanent magnet 12 and when the code bail is in a forward position the shunt 14 is pivoted between the ferromagnetic core 10 and the permanent magnet 12. The projections 20 on the bottom side of the key lever select a group of code bails that represent a particular character which is associated with the key that is depressed. After the key lever has been depressed, it is automatically moved forward pushing the selected code bails with it. This causes the shunts 14 to be moved between selected ferromagnetic cores and permanent magnets.

Whenever the shunt 14 is spaced away from the ferromagnetic core 10 and the permanent magnet 12, a groundlevel output voltage is provided to a computer associated wtih the core 10 by the drive circuitry 24. However, when a key has been depressed so that the shunt 14 is spaced between the ferromagnetic core and the permanent magnet 12, a 5 volt output voltage is provided to the computer by the drive circuitry 24. Each of the keys 16 cause a different pattern of 5 volt outputs to be provided to the computer when it is depressed in accordance with the code bails 22 that are selected by its respective key lever 18. In the alternative, the shunt may be normally spaced between the permanent magnet and the core. In this case, the shunt is moved away from the core and magnet when a corresponding key is depressed so that a ground level voltage on the output terminals indicates that the key has been depressed.

In FIG. 2, a schematic circuit diagram is shown illustrating the manner in which voltage outputs are provided at selected output terminals 26 by the transducer illustrated in FIG. 1. Each of the output terminals 26 has a transducer associated with it. A common driver transistor may be used for a multiple of transducers. There are eight output terminals in a typical keyboard arrangement so that the keys may be represented by an 8 bit output character. Readout of the 8 bit code is obtained by applying a positive voltage to the terminal 28 which is electrically connected to the base of the NPN transistor 30. This input voltage drives the transistor 30 into conduction, causing its emitter to be connected to ground in one path through the capacitor 32 and to ground in another path through the forward impedance of the two series connected diodes 31 and 33. The emitter of the transistor 30 is also connected to a source of a negative 14 volt through a resistor 34. Consequently, the emitter of the driver transistor 30 is negative with respect to ground y an amount 4 equal to the two forward biased junctions of diodes 31 and 33.

Each of the output terminals 26 is electrically connected to one end of an associated winding 36 around the ferromagnetic core 10. The other end of the winding 36 is connected to the collector of the transistor 30 through an isolation diode 38. Each of the. output terminals 26 is also connected to ground through the reverse impedance of a 5 volt Zener diode 40 and to a source 42 of a positive 24 volts through a resistor 44. The anode of the diode 38 is electrically connected to a source 45 of positive 24 volts through a 1K resistor 46. A single source may, of course, be used for the two sources 42 and 45. Each of the cores 10, of course, has a permanent magnet 12 adjacent to it and a movable shunt 14 adapted to be moved between the ferromagnetic core 10 and the permanent magnet 12 whenever a key is depressed.

Each of the cores 10 is inhibited from switching by flux from the permanent magnet 12 unless the shunt 14 is positioned between the permanent magnet 12 and the ferromagnetic core 10. This elect is explained more fully in the aforementioned patent application to Flavius A. Mathamel. If the core 10 is inhibited from switching because the shunt is not positioned between them, the coil 36 acts as a short between the junction of resistor 44 and Zener diode 40 to the collector of the transistor 30. Otherwise, it appears as a variable reactance which can be switched by the source 42 whenever the transistor 30 is conducting. The core 10 is reset to the opposite state by current from the source '45 which flows through the Zener diode 40 to ground when the transistor 30 is nonconducting.

The operation of the circuit shown in FIG. 2 will be explained more completely with reference to FIG. 3 which is a graph of a plurality of curves 48, 50, 52 and 54 having common abscissae of time and individual ordinates of voltage or current. The curve 48 shows a plurality of voltage clock pulses 56 which are the basic timing pulses for a computer that may be associated with the keyboard and transducers of this invention.

The curve 50 shows a voltage pulse 51 which is used to read out the keyboard between a specified two of the clock pulses 56 within a basic cycling frame typically of 16 clock pulses so that the depressed key is indicated once for every 16 clock pulses. The curve 52 illustrates the set voltage generated by the core 10 whenever a shunt 14 is positioned between the core 10 and the permanent magnet 12 and the pulse 50 is applied to the terminal 28, driving the transistor 30 to conduction to obtain a read out of the keyboard. The dotted portion 58 of the curve 5-2 indicates a typical voltage generated by a core which is being switched into a high impedance load.

However, in the circuit of this invention, the actual voltage generated is represented more closely by the curve 60 which has a long low voltage for approximately the same length of time as the pulse 50. This is obtained be cause the Zener diode 40 clamps the voltage at 5 volts so that the amount of current flowing from the voltage source 42 through the resistor 44 and the winding 36 to ground when the transistor 30 is conducting is controlled with surplus current flowing through the Zener diode 40 to ground. Of course, if the core is inhibited from switching because the shunt 14 has been moved between the ferromagnetic core 10 and the permanent magnet 12 by the depression of a key in the keyboard, there is no set voltage generated in the winding 36 by the switching of the core 10 and the waveform 52 will follow the dotted curve 62.

The curve 54 illustrates the voltage output at the terminal 26 with the dotted curve 64 representing the voltage output when a shunt is between the ferromagnetic core 10 and the permanent magnet 12 and with the solid curve 66 representing the voltage output when the shunt is spaced away from the ferromagnetic core 10' in the permanent magnet 12. During the time when the transistor 30 is non-conducting, the output voltage remains at a positive 5 volts where it is clamped by the Zener diode 40'. At this time the currents from both the positive voltage source 45 and the positive voltage source 42 flow through the Zener diode 40 to ground. The current from the voltage source 45 slowly resets the core 10, but no substantial reverse voltage is generated in the winding 36 by the resetting of the core 10. The maximum reset voltage possible is equal to the supply voltage.

If the shunt 14 is positioned between the core and the permanent magnet 12. when the pulse 50 is applied to the transistor 30, the core 10 is set by current flowing from the source 42 to the source of a negative 14 volts 35 through the resistor 34, or to ground in the case of the first wavefront through the capacitor 32 which is used to speed up the switching action. On the other hand, if the shunt 14 is not positioned between te core and the permanent magnet, the core 10 is inhibited from switching and no set voltage is generated in the coil 36. This causes the output terminal 26 to be at a level close to ground. Hence, it is connected to the negative source of voltage 35 through the forward resistance of the diode 38, the forward resistance of the conducting transistor 30, and the resistor 34. An AND gate connected to receive the read pulse 50 and the output from terminal 26 can be used to test for the presence of the 5 volt level that indicates a selected core.

It can be seen that the single transistor 30 controls a plurality of transducers to provide an output code at the plurality of terminals 26 indicating a particular key that is depressed in a keyboard. This transducer arrange ment is simple and economical, requiring only one ferromagnetic core and one winding for each transducer, even though the core is switched between its two permanent states by a single input pulse to the transistor 30. This is a substantial reduction in the number of components re quired for other general transducers. All of the components used are inexpensive and reliable.

What is claimed is:

1. A transducer comprising: a saturable reactor having a first terminal and a second terminal; a source of electrical potentional; a first impedance connecting said source of electrical potential to said first terminal of said saturable reactor; a second impedance connecting said source of electrical potential to said second terminal; switching means having first, second and third terminals, for connecting said second terminal of said saturable reactor to said first terminal of said switching means and through said switching means to an electrical sink coupled to said third terminal of said switching means upon receiving a signal on said second terminal of said switching means and for blocking the flo-w of current from said second terminal of said saturable reactor to said electrical sink upon receiving a signal on said second terminal of said switching means; and movable means having a first position and a second position for inhibiting the switching of said saturable reactor while said movable means is in said first position and for permitting the switching of said saturable reactor when said movable means is in said second position, whereby said saturable reactor is switched to a first saturated state when said second signal is applied to said switching means and said movable means is in said second position and said saturable reactor is switched to a second saturated state when said first signal is applied to said switching means and said movable means is in said second position.

2. A transducer in accordance with claim 1 in which said saturable reactor comprises a ferromagnetic core having a winding magnetically linking said core one end of which is electrically connected to said first terminal of said saturable reactor and the other end of which is electrically connected to said second terminal of said saturable reactor.

'3. A transducer in accordance with claim 2 further comprising: a second ferromagnetic core; a second winding magnetically linking said second ferromagnetic core having a first terminal and a second terminal; a second movable means having a first position and a second position for inhibiting the switching of said second ferromagnetic core when said second movable means is in said first position and for permitting the switching of said second ferromagnetic core when said second movable means is in said second position; said second terminal of said second winding being connected to said first terminal of said switching means and to said source of energy through a third impedance; said first terminal of said second winding being connected to said source of elec trical potential through a fourth impedance; a first output terminal connected to said first terminal of said first winding; and a second output terminal connected to said first winding; and a second output terminal connected to said first terminal of said second winding, whereby the electrical outputs on said first output terminal and said second output terminal respectively indicate the positions of said first movable means and said second movable means whenever said first signal is applied to said switching means.

4. A transducer in accordance with claim 3 in which said movable means and said second movable means each comprises: a permanent magnet positioned adjacent to an associated one of said ferromagnetic cores and a magnetitc-fiux shunt adapted to be moved from a position between said permanent magnet and said associated ferromagnetic core and a position spaced away from said permanent magnet and said associated ferromagnetic core.

5. A transducer in accordance with claim 4 further comprising: a plurality of key buttons forming a keyboard of an input device; each of said key buttons being rigidly connected to a different keystem; a plurality of code bails; and selection means connecting said keystems and said code bails for moving a different group of code bails from a first position to a second position each time one of said key buttons is depressed; each of said shunts being rigidly connected to a different one of said code bails, whereby said electrical outputs at said first and second output terminals are indicative of the depression of a unique key button in said keyboard.

6. A transducer in accordance with claim 5 in which said switching means comprises a transistor having its collector connected to said first terminal, its emitter connected to said third terminal, and its base connected to said second terminal.

7. A transducer in accordance with claim 6 in which said source of electrical potential comprises an electrical voltage source and said source of reference potential comprises an impedance in series with said source of electrical potential and having a more negative value of voltage than that of said source of electrical potential.

8. A transducer in accordance with claim 7 further comprising a first Zener diode having its cathode electrically connected to said first terminal of said first winding and having its anode grounded; a first diode having its anode electrically connected to said second terminal of said first winding and having its cathode electrically connected to said first terminal of said switching means; a second Zener diode having its cathode electrically connected to said first terminal of said second winding and having its anode grounded; and a second diode having its anode electrically connected to said second terminal of said second winding and having its cathode connected to said first terminal of said switching means.

9. A transducer for generating binary coded electrical signals in accordance with the mechanical positioning of a movable member, said transducer comprising:

a ferromagnetic core,

means for influencing the magnetic state of said core in accordance with the positioning of said movable member, said means including a magnet proximate said core, and

a movably mounted magnetic shunt. said shunt being selectively positionable relative to said magnet and said core in response to the movement of said movable member, common sense and reset winding means magnetically linking said core for sensing the magnetic state of said core and for resetting said core to a predetermined state, said winding means including first and second electrical terminals connected respectively to the ends of said winding means, and a current conductive switch means having at least two state of current conduction for establishing a sense current path through said winding means in a first direction when said switch means is in a first one of its two states of conduction and for establishing a reset current path through said winding in a direction opposite to said first direction when said switch means is in a second one of its two states of current conduction. 10. The transducer defined in claim 9 additionally having a first and a second resistor for respectively coupling said first and second terminals to a source of electrical potential, an output terminal, means for coupling said output terminal of said switch means to said first terminal, and reference means including a Zener diode coupled to and between said output terminal and a source of reference potential for clamping said output terminal to a predetermined potential.

11. A system for controlling the generation of an electrical pulse comprising a single transducer winding connected at one end thereof in a closed circuit to a source of direct current for current flow in one direction, a single magnetic core having said single winding thereon, said core saturable in a reset sense upon flow of current through said single winding in said one direction, a magnet positioned adjacent said core and normally inhibiting pulse output from said winding, means operable to render said magnet ineffective to inhibit pulse output from said winding, and switch means electrically connected to said one end of said winding and through said winding to the current source, said switch means operable when closed to elfect flow of current from said source through said winding in a direction opposite to said one direction to saturate said core in a set sense when said means renders said magnet ineffective.

References Cited UNITED STATES PATENTS 3,305,770 2/1967 Hulls 32389 ALVIN H. WARING, Primary Examiner Us. 01. X.R. 340-174; 307-314 

